In sea urchin DNA, which is double-stranded, 17 % of the bases were shown to be cytosine. What are the…

In sea urchin DNA, which is double-stranded, 17% of the bases were shown to be cytosine. What are the percentages of other three bases expected to be present in this DNA?
  1. G=34%, A=24.5%, T=24.5%
  2. G=17%, A=16.5%, T=32.5%
  3. G=17%, A=33%, T=33%
  4. G=8.5%, A=50%, T=24.5%

Solution

In the DNA molecule, the nucleotides are base paired according to the Chargaff's rule of base equivalence, and it tells always tells adenine pairs with thymine and guanine pairs with cytosine.
A = T, G = C
C = 17% So G = 17%
A+G / T+C =1
A + G + C + T = 100
A + 17 + 17 + T = 100
A + T = 100 - 34
So, A = 33%, T = 33% = 66

Asked in: NEET 2015 (Phase 1)

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